There is known a technology of forming a low-impurity-concentration area by implanting an impurity into a first area, which is outside an area corresponding to a channel area in a semiconductor layer, after forming a gate electrode, and forming a source/drain area by implanting an impurity at high concentration into an outside portion of the first area after covering the low-impurity-concentration area with a resist mask.
Also known are a technology of forming a lightly-doped-drain (LDD) thin-film transistor by, using a resist as a mask, implanting an impurity, and further implanting an impurity after removing the resist; and a technology of changing the film thickness of a resist by exposing the resist with a halftone mask.